| OCR Text |
Show Figures 190-19 7 are computed spectra and coherences between the precipitation rate series and a one cycle per hour square wave, for both seeded and unseeded combined series for four of the major line of ridge stations. The fundamental frequency of 0. 01667 cycles per minute is the frequency ' of the forcing function. For the Buffalo Pass unseeded and seeded series the coherence values are well below the 5% significance level and there are no significant peaks in the spectral curves. The coherence curves for Long Lake at the fundamental frequency just peak to the 5% significance level for both the seeded and the unseeded series. The Base Camp coherence curve , is below the 5% significance level for the unseeded series and is also below this level for the seeded series, except for the first odd harmonic at 0. 05 cycles min. - l. The coherence curves for Rabbit Ears are of particular interest. In Figure 197 the coherence value for the fundamental frequency peaks above the 5% significance level; it is also supported by a slight peak .. in the spectral curves. In Figure 196 the coherence for the unseeded series also peaks slightly above the significance level, but the coherence is not supported by a peak in the spectral curve. All of the data were also analyzed as short spectra of indi victual storms. An example of the results obtained is typified by analysis period number 12 on - 20 December 1967. The forcing function was applied from Emerald Mountain as a square wave at 0. 5 cycles hr. -l. The upper air winds measured at Mt. Harris varied from 280-300 degrees and 10-17 knots at 11·, 000 ft. MSL. The free air nuclei count measured at Rabbit Ears Pass was w·e n above background levels through the period. The atomic absorption analysis of serial snow samples taken at Rabbit Ears Pass showed silver content well above background levels, and displayed a periodic characteristic. Two soundings taken at Mt. Harris during the period were characterized by unstable lapse rates and a fairly thin cloud layer extending from -11 to -25°C at 1630 MST. The vertical diffusion of aerosol should have been rapid. All indications are that there should have been a positive seeding effect at the southern end of the ridge line of network stations. 1111 1 The coherence values for a group of stations at either end of the network are displayed in Figure 198. None of the coherence values at the fundamental frequency of 0. 00833 cycle mino -l are above the 5% significance level. The values at the odd harmonics of this frequency are definitely higher for the southern, or seeded, station group. Cross correlation coefficients between the precipitation rate time series and the time series of free air nuclei count were computed for Rabbit Ears Pass, using the same groups of stations as for the curves of Figure 198. Th~s~ are Note from Figure 199 that the coeff1c1ents ~! presented in Figures 199 and 200. are negative, and remain negative with lag times to 70 minutes; the southern network group in Figure 200 peak at high positive values at lag times of from ia l: 35 to 75 minutes. Note in particular Valley View, where the peak occurs at 279 |
